The functional anatomy of the lower extremity represents a complex integration of structural adaptations for bipedal locomotion, weight-bearing, and dynamic stability. This chapter provides a comprehensive examination of the lower extremity’s anatomical organization, emphasizing its neuromuscular control, biomechanical principles, and functional relationships. The developmental aspects of the lower limb, including its characteristic 180° medial rotation, establish the foundation for understanding its adult configuration and function. The neural framework, primarily derived from the lumbar and lumbosacral plexuses (L1–S4), creates an intricate network that enables precise motor control and systematic sensory distribution through dermatomes. The chapter explores the distinct architectural features that differentiate the lower extremity from the upper limb, particularly highlighting the robust pelvic girdle-sacrum connection and the deep acetabular socket of the hip joint. Each major joint complex—hip, knee, and ankle-foot—is analyzed in terms of its structural components, stabilizing mechanisms, and functional contributions to locomotion. Special attention is given to the muscular systems that control these joints, from the powerful hip musculature to the intricate foot intrinsics. The ankle–foot complex receives detailed consideration, particularly regarding its role in shock absorption, propulsion, and adaptation to varying surfaces. The text emphasizes the dynamic interplay among skeletal architecture, ligamentous support, and muscular control in maintaining the foot’s arched structure and enabling efficient force transmission during gait. Understanding these anatomical and functional relationships is crucial for healthcare professionals involved in rehabilitation, sports medicine, and orthopedics, as it forms the basis for clinical decision-making and therapeutic intervention strategies. Throughout the chapter, clinical correlations illuminate the practical implications of anatomical principles, particularly in the context of common pathologies and rehabilitation approaches. The integration of developmental, structural, and functional perspectives provides a comprehensive framework for understanding the lower extremity’s role in human movement and posture.